[codex] Suppress audio firewall warning after allow

[Balragon]

Summary

• Remember a successful in-app Windows Firewall allow action for the current process.
• Before showing the delayed audio RTP firewall warning, check whether an enabled inbound allow rule already exists for the current iMirror executable.
• Suppress the warning when the rule is already present, so users are not repeatedly asked to allow audio after they have already allowed iMirror.

Why

The v0.7.2 fix cleared the warning immediately after the Allow flow completed, but the startup watchdog could show the same warning again later if audio RTP was delayed or absent. That made the warning feel stale after the firewall rule had already been installed.

Validation

• dotnet build .\iMirror.sln -c Release --no-restore -p:OutDir=artifacts\verify\out\ passed with zero warnings and zero errors.
• dotnet test .\MacMirrorReceiver.Tests\MacMirrorReceiver.Tests.csproj -c Release --no-restore -p:OutDir=artifacts\verify\testout\ passed: 65 tests.

Notes

The first direct build to the normal Release output was blocked because the local test iMirror process was still running from the previous visual validation and held bin\x64\Release\net10.0-windows\win-x64\iMirror.exe. The successful build used an alternate output directory to avoid interrupting the running app.